1. Field of the Invention
This invention relates to method and composition for affixing a dental appliance to teeth. More particularly, this invention relates to method and composition for bonding directly to the teeth to facilitate affixing a dental appliance thereto.
2. Description of the Prior Art
The prior art has seen a wide variety of orthodontic corrective procedures to align mal-occluded teeth in humans and the like. Most of these corrective procedures employed a dental appliance in one way or another to correct improper growth of the teeth and the like. The term "dental appliance" is employed in its broad sense in this application to signify any of the appliances whether to correct the growth of teeth, bridging of the teeth and the like. Such dental appliances typically include braces, space maintainers, splints, bridge works of more elaborate type and any other type of device that will be affixed to one or more of the teeth in the mouth with the objective of supporting or affecting the action or growth of other teeth.
A major orthodontic corrective procedure to align mal-occluded teeth is the placement of metal bands around individual teeth and thereafter affixing the remainder of the dental appliance to these metal bands. The metal bands may have affixed bases or brackets, sometimes referred to as the fixed appliance, or part thereof. Wires having high-tensile strength are then attached to the metal bands and the fixed portion of the appliance and then to the remainder of the appliance and teeth to affect proper tooth movement through the action of the wire itself or of springs or spurs attached to the wire. The affixed appliances, or brackets, require precise positioning to effect proper tooth movement.
Adhesive bonding of the affixed appliances to tooth surfaces is the ultimate in this type of orthodontic practice in order to eliminate the tedious band fitting procedure and to greatly reduce the decalcification of teeth and the gingival damage that all too frequently occurs with banding. Moreover, bonding with a resin type adhesive facilitates cleaning by the patient with less opportunity for food accumulation and consequent tooth decay compared to the banding because most of the appliances are at the front surface of the teeth in adhesive bonding with greater accessibility for cleaning.
Despite the advantages of adhesive bonding, it has not achieved universal success because of the inconsistent results from the currently available bonding orthodontic adhesives and the techniques, or methods, of using them.
Currently available orthodontic bonding adhesives generally use one of two techniques for applying orthodontic appliances to the teeth. In each of the techniques the teeth are prepared by cleaning, acid etching, washing and drying.
In the first technique, the bonding resin co-monomer is not mixed with a catalyst but is applied to a clear, transparent plastic bracket that is precisely positioned on the dried tooth surface. An ultraviolet light is directed onto the clear bracket so as to penetrate through to initiate polymerization of the bonding resin. In this way, the viscosity of the resin co-monomer can be adjusted to optimize wetting and avoid creeping but the requirement for a clear, light-penetrating material for a bracket limits the strength of the bracket, which are generally inferior to the stainless steel brackets otherwise employed. Consequently there are frequent failures due to inadequate structural strength to resist the stress of the attachment; for example, force by high-tensile strength wire. The ultraviolet light itself, if used indiscriminately, is known to produce skin cancer, especially on soft tissue. Consequently, many orthodontists favor another procedure.
Another procedure comprises admixing the exact proportions of an adhesive formulation consisting of filler, catalyst, co-monomer resin and accelerater on a cold plastic slab, or glass plate and the like. The mixing of the catalyst and co-monomer initiates polymerization of the co-monomer resin immediately so the orthodontist has limited working time to coat the several bases of the brackets, or portion of the appliance to be bonded to the teeth, and to precisely position it on the prepared teeth surfaces. Also, the viscosity of the resin is continuously changing with the degree of polymerization. This affects positioning and creep of the brackets, as well as the ultimate bond strength. Viscosity also varies as the proportions of resin and catalyst are varied, deliberately or carelessly. For example, if the amount of catalyst in relation to the resin is too large, polymerization is too rapid and the higher viscosity of the resulting resin will cause inadequate wetting of the surfaces of the teeth and bracket base. Good wetting onto clean surfaces is the most important criterion in forming strong bonds. The result is a weak bond at best and ultimate displacement of the appliance from the tooth. On the other hand, if the proportion of catalyst is too small, the resulting mixture prepared by the orthodontist or his assistant has a low viscosity due to slow polymerization. This results in "creeping" of the appliance from its optimum placement position on a respective tooth. If attempts are made to reposition a bracket, or portion of an appliance, after "creep," then the bond is weakened and the appliance will ultimately be displaced from the tooth.
From the foregoing, it can be appreciated, that the prior art has not been totally satisfactory in solving the problems. First, a thorough mixing of exactly the right proportions of the adhesive is a requirement in order to evenly disperse the catalyst. Second, even a properly proportioned admixture forces the orthodontist to work in a limited time frame without the luxury of being able to correct for unanticipated delays or contingencies. Otherwise he must begin anew, with wasting of time and expensive adhesive.
Idealy, a bonding method and formulation would have the following features:
1. The bonding formulation and method should avoid the use of ultraviolet light or carcinogenic agents.
2. The bonding method or composition should allow relative freedom of the dentist to be as precise in placement and as careful in maintaining the bracket, or base of a dental appliance, in position to avoid creep as he wishes, without having to work within a time constraint.
3. The bonding method and composition should provide a relatively constant viscosity that is optimal for effectively wetting the surfaces of the teeth and of the dental appliance that is to be bonded to the teeth; simultaneously avoiding creep of the bracket, or portion of the dental appliance to be bonded to the teeth.
4. The bonding method and composition should obviate the necessity for careful admixing of predetermined portions so as to be operable even at moments of carelessness by the orthodontist or assistant.
5. In specific embodiments, the bonding method and composition should be operable by either direct bonding or indirect bonding techniques if the latter are desired to speed up the affixing of the dental appliance.
6. Moreover, in specific aspects, the bonding method and composition should provide a means that will facilitate application of one or more of the ingredients to the portion of the dental appliance that is to be bonded to the teeth to eliminate the care of having to wet that portion of the dental appliance.
7. The bonding method and composition should facilitate using complementary advantageous method steps; such as, forming shields or sealant layers, over the teeth to minimize decay.